On average the Venetians who lived during the glory days of the Republic were rather small, just five feet five inches in height; they were well nourished, and if they lacked sugar and fat the result was excellent teeth with no cavities.

These are among the first findings of a group of archaeologists exploring a treasure trove of Venetian history that has been locked away and forgotten for centuries: the graves of Lazzaretto, an island in the Venetian lagoon whichbecame the world’s first isolation hospital.

Following an outbreak of the plague in 1348, the Doge and his advisers put their minds to thinking up a way to prevent a recurrence. The upshot, at the beginning of the 15th century, was the world’s first isolation hospital occupying the entire small island.

In 1630 the hospital was dissolved and the island taken over by a military garrison; later it was used to hold stray dogs. In the 1960s it was abandoned altogether.

Now it has become the subject of intensive study. Backed by Consorzio Venezia Nuova, the quango directing the building of the underwater gates designed to protect Venice from flooding, the archaeologists have uncovered more than 1,500 skeletons of Lazzaretto patients. Luigi Fozzatti, who is in charge of excavations, said: “It wasn’t difficult to imagine that some people would have been buried on the island but we had no idea we would find so many.”

The first grave was found when the excavators began clearing away rubble for the rebuilding of one of the sheds. Since then more than 240 have come to light, some crowded with skeletons, some housing only a few. To date 1,560 individual skeletons have been found, dating from four, five and six centuries ago, most of them in perfect condition.

“With the research they will undergo in the laboratory, they will yield a mountain of information without precedent,” the anthropologist Luisa Gambaro of the University of Padua told La Repubblica newspaper.

Already a picture of the harsh lives of some of those confined here is beginning to emerge. A number of the patients were afflicted with a disease called Schmorl’s Node, a type of hernia caused by heavy stress on the back – probably the occupational hazard of the porters who lugged Venice’s merchandise around on their backs.

Yet although these skeletons by definition belonged to people who were extremely sick, they were remarkably fit.

Some had arthritis, some tuberculosis, some had fractures that had healed badly, but in general they seem to have enjoyed a nutritious diet and a healthy lifestyle.